The purpose of this project is to provide an independent surveillance of the health status of rats maintained in contractor facilities for the nine-year hybrid rat colony. One hundred rats per year selected by the Project officer, are to be shipped from the NIA colony to an independent laboratory for health and pathology evaluation. The Project Officer will select animals from the inventory maintained in the NIA Resource Development Office which effectively samples the range of ages and holding rooms that characterize the colony. The evaluation to be performed will include: -Gross Pathology: observation of organs and tissues for gross pathological lesions. -Histopathology: lung, liver, kidney, spleen, brain, and abnormal tissue from gross pathology. -Microbiology: mycoplasma, salmonella, pseudomonas, any abnormal discharges, exudates or inflammatory process. -Parasitology: endoparasites, ectoparasites. -Serology: rat viruses. -Clinical Chemistries: sodium, Potassium, serum electrophoresis, total protein, A/G ratio, cholesterol, creatinine, glucose, CBC. Complete postmortem reports on individual animals shall be submitted to the Project Officer no later than three months from the date the animals are submitted for evaluation. This project is not intended to provide a statistically significant sample of the colony population, but rather to provide a resource to the Project Officer to monitor colony contractor performance and to provide an independent assessment of animal health when needed.